Transformation of ceria nanoparticles in cucumber plants is influenced by phosphate

Transformation is a critical factor that affects the fate and toxicity of manufactured nanoparticles (NPs) in the environment and living organisms. This paper aims to investigate the effect of phosphate on the transformation of CeO₂ NPs in hydroponic plants. Cucumber seedlings were treated with 2000 mg/L CeO₂ NPs in nutrient solutions with or without adding phosphate (+P or –P) for 3 weeks. Large quantities of needle-like CePO₄ was found outside the epidermis in the +P group. While in the –P group, CePO₄ only existed in the intercellular spaces and vacuole of root cells. X-ray absorption near edge spectroscopy (XANES) indicates that content and percentage of Ce-carboxylates in the shoots of –P group (418 mg/kg, 67.5%) were much higher than those in the +P group (30.1 mg/kg, 21%). The results suggest that phosphate might influence the transformation process of CeO₂ NPs in plants and subsequently their ultimate fate in the ecosystem.